Mycobacterial infections can cause different diseases such as tuberculosis. Additionally, mycobacterial diseases can cause overwhelming, disseminated disease in immunocompromised patients. In spite of the efforts of numerous health organizations worldwide, the eradication of mycobacterial diseases has never been achieved, nor is eradication imminent.
Nearly one third of the world's population is infected with Mycobacterium tuberculosis complex, commonly referred to as tuberculosis, with approximately 8 million new cases, and two to three million deaths attributable to tuberculosis yearly. Tuberculosis is the cause of the largest number of human deaths attributable to a single etiologic agent. After decades of decline, tuberculosis is now on the rise. In the United States, up to 10 million individuals are believed to be infected. Almost 28,000 new cases were reported in 1990, constituting a 9.4 percent increase over 1989. A sixteen percent increase in tuberculosis cases was observed from 1985 to 1990. Overcrowded living conditions and shared air spaces are especially conducive to the spread of tuberculosis, contributing to the increase in instances that have been observed among prison inmates, and among the homeless in larger U.S. cities.
Approximately half of all patients with “Acquired Immune Deficiency Syndrome” (AIDS) will acquire a mycobacterial infection, with tuberculosis being an especially devastating complication. AIDS patients are at higher risks of developing clinical tuberculosis, and anti-tuberculosis treatment seems to be less effective than in non-AIDS patients. Consequently, the infection often progresses to a fatal disseminated disease. Mycobacteria other than M. tuberculosis are increasingly found in opportunistic infections that plague the AIDS patient. Organisms from the M. avium-intraceliulare complex (MAC), especially serotypes four and eight, account for 68% of the mycobacterial isolates from AIDS patients. Enormous numbers of MAC are found in the patients, thus, the prognosis for the infected AIDS patient is poor.
Although over 37 species of Mycobacterium have been identified, more than 95% of all human infections are caused by six species of mycobacteria: M. tuberculosis, M. avium intracellulare, M. kansasii, M. fortuitum, M. chelonae, and M. leprae. Cases of human tuberculosis are predominantly caused by mycobacterial species comprising M. tuberculosis, M. bovis, or M. africanum. Infection is typically initiated by the inhalation of infectious particles, which are able to reach the terminal pathways in the lungs. Following engulfment by alveolar macrophages, the bacilli are able to replicate freely, with eventual destruction of the phagocytic cells. A cascade effect ensues wherein destruction of the phagocytic cells causes additional macrophages and lymphocytes to migrate to the site of infection, where they too are ultimately eliminated.
The emergence of drug-resistant M. tuberculosis is an extremely disturbing phenomenon. The rate of new tuberculosis cases proven resistant to at least one standard drug has increased. Compliance with therapeutic regimens, therefore, is also a crucial component in efforts to eliminate tuberculosis and prevent the emergence of drug resistant strains. Equally important in the development of new therapeutic agents that are effective as vaccines, and as treatments, for disease caused by drug resistant strains of mycobacteria. Mycobacteria can be classified into several major groups for purpose of diagnosis and treatment: M. tuberculosis complex (MTBC), which can cause tuberculosis (M. tuberculosis, M. bovis, M. africanum, and M. microti); M. leprae, which causes Hansen's disease or leprosy; and Nontuberculous mycobacteria (NTM) are all the other mycobacteria, which can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, or disseminated disease. MTBC members are causative agents of human and animal tuberculosis. Species in this complex include: M. tuberculosis, the major cause of human tuberculosis M. bovis, M. bovis BCG, M. africanum, M. canetti, M. caprae, M. microti, and M. pinnipedii. 
Multidrug-resistant tuberculosis (MDR-TB) is a form of tuberculosis that is resistant to two or more of the primary drugs used for the treatment of tuberculosis. Resistance to one of several forms of treatment occurs when bacteria develop the ability to withstand antibiotic attack and relay that ability to their progeny. Because an entire strain of bacteria inherit this capacity to resist the effects of various treatments, resistance can spread from one person to another.
Clearly, the possibility of drug resistant strains of tuberculosis that develop during or before treatment are a major concern to health organizations and health care practitioners. Drugs used in the treatment of tuberculosis include, but are not limited to, ethambutol (EMB), pyrazinamide (PZA), streptomycin (STR), isoniazid (INH), moxifloxacin (MOX), and rifampicin (RIF). The exact course and duration of treatment can be tailored to a specific individual, however several strategies are well known to those skilled in the art.
In 2003, the CDC reported that 7.7 percent of tuberculosis cases in the U.S. were resistant to INH, a first line drug used to treat tuberculosis. The CDC also reported that 1.3 percent of tuberculosis cases in the U.S. were resistant to both INH and RIF. RIF is the drug most commonly used with INH.
The standard treatment for tuberculosis caused by drug-sensitive organisms is a six-month regimen consisting of four drugs given for two months, followed by two drugs given for four months. The two most important drugs, given throughout the six-month course of therapy, are INH and RIF. Although the regimen is relatively simple, its administration is quite complicated. Daily ingestion of eight or nine pills is often required during the first phase of therapy; a daunting and confusing prospect. Even severely ill patients are often symptom free within a few weeks, and nearly all appear to be cured within a few months. If the treatment is not continued to completion, however, the patient may experience a relapse, and the relapse rate for patients who do not continue treatment to completion is high.
There is a long felt need in the art for new and improved antimicrobial agents. The present invention satisfies these needs.